Data Recovery and Disk Utilities Forum @R-TT

I installed the R Undelete (unpaid) and tried to recovered some of the deleted files in the SD card. The software scan through the entire SD card successfully and required me to select the files from the table. I tried to recover those files with name started with $, but the recovered files after renamed cannot be viewed successfully. I checked these files with a HEX viewer, and noted that the binary code are all "0", the ANSI, OEM, and Unicode columns are all marked with dots. But, the files indicated in the explorer are not zero.
Some of the avi files recovered with the name of numbers only cannot be viewed successfully as well.

Does it means that these files have been deleted long time ago, and the positions had been replaced by others, so they cannot be recovered.

It's hard to say without seing the actual data on the card. Most likely, files with 0s are indeed overwritten, and the avi files were fragmented.